The patella is a sesamoid of lens shaped bone which slides in a groove between the condyles of the femur. Its function is to increase the efficiency of the quadriceps muscle by shifting the line of action of the muscle's pull forward. As the knee articulates, the muscles and tendons force the patella toward the condyles of the femur. Consequently, there is considerable relative motion between the patella and the other bones comprising the knee joint.
Because of aging, disease or sporting activities, the articulating surfaces of the knee may degrade. To treat certain pathologies, it has become common to surgically remove the condyles and replace these structures with prosthetic implants. By the same processes, the articulating surfaces of the patella may also be replaced. Because of the tendons connected to the patella, it is generally advisable to replace only the articulating surface. A patella button made of ultra high molecular weight polyethylene with an articulating surface, with or without a metal base plate has been used to replace the posterior or interior side of the patella, adjacent the femoral condyles. To implant such a prosthesis, the posterior surface of the patella is resected to produce a flat surface on which the prosthesis can be mounted.
The process of cutting, drilling and replacing the damaged surface of a patella is complex, awkward and time consuming. The process requires three separate basic steps:
1) Resecting or removing the damaged posterior articulating surface of the patella; PA1 2) providing means in the resected patella for receiving the prosthesis; and PA1 3) attaching the prosthesis to the resected and prepared patella. PA1 a) a top and a bottom combination prong and handle members with a fulcrum therebetween and having a posterior and anterior surface, the prong and handle members being pivotably mounted in relation with one another at the fulcrum with a hinge bolt, said hinge bolt extending through holes at the fulcrum and having a rotatably adjustable knob thereon to maintain a set distance from the posterior surface of the top prong and handle member; PA1 b) means along the inner edges of the prong members for firmly holding the periphery of a patella, with the posterior surfaces of the prong members defining the plane along which the patella is to be resected; PA1 c) a locking device at the ends of the handle members opposite the prong members to enable locking of the prong members to maintain a firm hold around the periphery of the patella; PA1 d) a tongue member attached to a prong member near the fulcrum of the device and positioned between the prong members and at a predetermined distance from the anterior surface of the prong members for engaging the anterior surface of the patella thereby controlling the depth to which the patella is to be resected; PA1 e) a drill guide consisting of a member having holes therethrough with an attached slotted member, the slot being of a suitable width and thickness to be slidably insertable between and removable from the knob of the hinge bolt and the posterior surface of the top handle member and to fit snuggly around the post of the hinge bolt; and PA1 f) a patella button presser consisting of an S-shaped bar having at one end a slotted tongue member and at the opposite end a hole with a bolt inserted therethrough with means to control the up-and-down movement of the bolt through the hole, the tip of the bolt having a platen movably mounted thereon, the platen having a concave surface for engaging the convex surface of the patella button, and said patella button presser being slidably insertable between and removable from the hinged bolt knob and the posterior surface of the top handle member.
To accomplish these three steps, several separate devices are employed. These include a device for firmly holding the patella to expose its posterior surface; a saw; a saw guide to control the portion of the patella that is to be removed; a drill to provide means to attach the implant securely; a drill guide to control the placement and depth of the means for attaching the prosthetic implant; and a device to insert the prosthesis and press the prosthesis into place. This latter device ensures that the attachment of the prosthesis with the resectioned patella is secure.
Devices for such a process have been developed and described. In particular, clamp-like patella resection and replacement devices have been described in U.S. Pat. Nos. 4,633,862; 5,002,547; 5,108,401; 5,129,908; 5,147,365; 5,542,947; 5,716,360; and 5,716,362.
U.S. Pat. No. 4,633,862 described two clamps: one to resection and drill holes in the patella and one to insert and press the prosthesis into place. Tongue members were provided on the first clamp for controlling the depth for resection of the patella. After which, the patella was released for the mounting of a drill guide onto the clamp. The drilled patella was again released, and a second clamp provided with a plunger was used to insert, press and cement the prosthesis to the cut patella.
The clamps that are in use or known are quite bulky and awkward to use. Moreover, at each step of the process, the patella must be released for the detachment and installation of the various implements, such as the saw guide and the drill guide, and the use of the second clamp for the implanting the prosthesis. These maneuvers necessitate the re-positioning and re-orientation of the patella at each of the step of the process. For this reason, the process for resection and replacement of a patella is not efficient.
U.S. Pat. No. 5,002,547, disclosed a total of 14 different devices for surgery of the knee. Among which, a clamp with separately mountable modular patella resection guide, drill guide and prosthesis attachment was shown. The prong members of the clamp were provided with a quick disconnect mechanism for attaching separately a resection guide, a drill guide and a prosthesis presser. Because of the need to mount the resection guide, the drill guide and the prosthesis presser on the prong members of the clamp, it is still necessary to re-position and re-orient the patella with the clamp at each step.
A pliers-like device with jaw members for holding a patella securely for resection is described in U.S. Pat. No. 5,108,401. The device was provided with an elevator member to engage the anterior surface of the patella held at a predetermined distance between the elevator member and the jaws members to ensure that the cut is made at an appropriate thickness. There is no description of a drill guide or a presser for securing the patella prosthesis to the resected patella. This means that additional implements would be needed for drilling the patella and for implanting the prosthesis.
U.S. Pat. No. 5,129,908 disclosed a clamp for holding and reaming a patella to provide a centrally raised portion for fixation of a prosthesis. The clamp was provided with a C-like jaw member and an L-shaped jaw member. The C-shaped jaw member has a spiked platform for engaging and holding the anterior surface of the patella with a reamer guide detachably connected to a plunger mounted on another arm of the C-shaped jaw member. The distance of the reamer guide from the platform was adjustable to accommodate patellas of different sizes. In this device, a reamer is used to remove a portion of the posterior surface of the patella in a rotary manner. The position of a reamer guide controls the depth to which the cut is made. The '908 patent further disclosed a drill guide added to the reamer guide. The Petersen '908 patent does not include presser clamp or device for the implantation of a prosthesis.
U.S. Pat. No. 5,147,365 also disclosed a pliers-like device for clamping and guiding a sagittal saw for the resection of a pre-determined portion of the patella. A rotating, calibrated stylus measures the position of the patella with respect to the integral sagittal saw. Capture slots are provided in each of the jaw members through which the sagittal saw may be mounted. The stylus and a draw bar served as a saw guide. The stylus and draw bar assembly comprised a scale bushing which fits through bores provided at the fulcrum of the clamp. The stylus arm carried a scale post, which could be adjusted vertically. This enables the surgeon to determine the precise amount of the patella, which is to be removed. There is no disclosure of a drill guide or a prosthesis presser.
U.S. Pat. No. 5,542,947 disclosed a clamp with a resection guide and stylus for the patella. The clamp was provided with a pair of tooth-edged jaw members for holding the patella. A plurality of calibrated and marked slots located at different fixed predetermined heights above the resection level is integrally formed on the jaw members. Each slot was provided with a saw blade insertion guide and a removably attachable stylus. The stylus is employed to select the slot for setting the resection depth. After the slot was selected and the saw blade inserted, the stylus may be detached to provide more visibility for the surgeon. The clamp was provided with a spring biased pivot to maintain the jaw members in a closed position and an adjustable locking means on the handles to lock the relative position of the jaw members. There is no disclosure of a drill guiding clamp nor a prosthesis presser clamp.
U.S. Pat. No. 5,716,360 described an instrument to resection a patella into different shapes: oval, tri-oval, or elliptical to receive a patella prosthesis of like shape. The patented device was a clamp with up-and-down jaw members for gripping the patella firmly for resection. It is clear that the resection instrument described in the '360 patent device is different from the present invention.
U.S. Pat. No. 5,716,362 described a patella-milling instrument having a base member with a handle assembly. A clamping element was slidably mounted on the base component. The support arm of a milling tool was slidably mounted on a post extending perpendicularly from the base member. The driving motor for the milling tool is mounted at the end of the arm to rotate the milling tool, or move it up and down. The '362 patent does not describe a clamp that is useful for drilling holes in the resected patella nor for pressing the patella prosthesis to engage with the resected patella.
The problems encountered in connection with the use of existing devices, generally known as "patella clamps" are several.
Many of the existing devices for patella replacement surgery are in the form of plier-like clamps. The clamp is used to securely hold the patella during surgery. The clamp is provided with a saw guide to ensure that the depth of the resection is appropriate and the resulting cut surface is even. After the damaged articulating posterior portion of the patella is removed, holes are drilled into the resectioned patella to receive the posts provided on the patella button. To ensure that the size and depth of the drill hole is appropriate, another clamp is provided with a drill guide or a drill guide attachable to the clamp jaw members is used.
The use of another clamp or the attachment of a drill guide to a clamp jaw member of a patella resection and replacement device requires the release and re-clamping of the patella. After the holes are drilled, the patella button or prosthesis is placed against the resectioned surface of the patella with its posts engaging the holes drilled into the resectioned patella. The prosthesis is pressed against the patella to ensure a tight fit of the posts into the drilled holes and to cement the surface of the prosthesis to the cut patella. In this step, the patella is again released from the clamp and a patella clamping or pressing device ("the prosthesis presser") is used. The release and re-clamping of the patella means that the position of the patella needs to be re-oriented at the beginning of each step of the operation.
Furthermore, most of the existing patella clamps are rather large and bulky. When in use, the device blocks the surgeon's view and prevents physical access to the joint. This is a particularly acute problem when the patella prosthesis is being cemented and pressed into the resected patella. The surgeon must wait until the prosthesis is cemented into place before continuing with the operation, thereby causing delay. Moreover, some of the existing patella presser clamps are provided with rather long handles to improve the mechanical advantage. However, this increases the risks of fracturing the patella during the operation, a very undesirable occurrence.